MEPS 370:97-109 (2008)  -  DOI: https://doi.org/10.3354/meps07661

ABSTRACT: Smothering of many fringing coral reefs in Indonesia has led to mangrove colonization of the overlying soils in a process of human-induced succession. On the islands of Sulawesi and Sumatra, we measured some structural and functional attributes of 4 mangrove forests that have colonized such soil drapes. The forests varied extensively in stem density, above-ground biomass, and in leaf area index. We estimated accumulation rates of above-ground forest biomass of 1.5 to 8.1 t C ha^–1 yr^–1, similar to other mangroves. The ratio of greenhouse C and N emissions from soils averaged 35 compared with an average soil C:N ratio of 38. Soil ammonification was sufficient to meet forest N demand. A value of 1 to 4% of soil C metabolism was involved in dissolving carbonate, with sulfate reduction being the major decomposition pathway. Rapid rates of N₂ loss were measured, but there was no detectable N₂O release. Rates of nitrogen fixation on the soil surface ranged from 97 to 1648 µmol N m^–2 d^–1, but higher rates (860 to 4316 µmol N m^–2 d^–1) were measured on microbial mats covering pneumatophores, suggesting N₂ fixation on above-ground tree parts may balance soil N₂ losses. Rates of forest biomass accumulation related exponentially to rates of soil C and N metabolism, reflecting a close relationship between tree growth and nutrient availability as mediated by microbes in these shallow soils. These patterns are similar to those in other mangrove forests, and illustrate that human-induced change has resulted in a clear shift from reef-dominated to mangrove-dominated habitats and functional characteristics in parts of coastal Indonesia.

KEY WORDS: Carbon · Greenhouse gases · Mangrove · Nitrogen · Indonesia